1. Field of the Invention
The present invention generally relates to demodulating methods and receiver apparatuses, and more particularly to a demodulating method which demodulates a received signal received by a receiver apparatus by detecting an absolute phase of signal points, and a receiver apparatus which employs such a demodulating method.
2. Description of the Related Art
In communication systems such as digital satellite broadcast systems, the communication is made by employing a digital modulation technique such as the BPSK, QPSK, nPSK and nQAM. In such communication systems, the signal modulated by the digital modulation technique is demodulated in a digital demodulator unit of a receiver apparatus, but in general, the detection of the absolute phase becomes uncertain at the time of the demodulation.
FIGS. 1 and 2 respectively are diagrams for explaining the detection of the absolute phase when demodulating a signal which is demodulated by the 8PSK. If it is assumed that FIG. 1 shows the correct positions of data 1 through 8, a normal digital demodulator unit cannot judge such correct positions of the data 1 through 8, and can only judge the positions where the data should stop. For this reason, even if the positions where the data should stop are correct, the positions of the data 1 through 8 may deviate by 45 degrees from the correct positions as shown in FIG. 2, for example. In this case, with respect to the correct positions of the data 1 through 8 shown in FIG. 1, a total of 8 possible patterns could occur as the phase error, including the pattern shown in FIG. 2.
Conventionally, in order to detect the phase error described above, it is necessary to successively detect the 8 phases. According to a normal phase error detecting method, if the received signal is made up of synchronizing signals and data as shown in FIG. 3 and a number of regularly incoming synchronizing signals which are consecutively detected reaches a set value, it is regarded that 1 phase of the data is detected. All of the 8 phases are detected in a similar manner.
Generally, the synchronizing signal is made up of several bits. This is because, if the number of bits forming the synchronizing signal is small, the possibility of a signal having a pattern identical to that of the synchronizing signal being accidentally generated in a data sequence increases. For this reason, when a reception state of the receiving unit is poor due to the weather conditions or the like and considerable error is generated in the received signal due to noise, error is also inevitably generated in the synchronizing signal. When the error is generated in the synchronizing signal, it takes time to detect the synchronizing signal, and in an extreme case, it may become impossible to detect the synchronizing signal.
In the conventional receiver apparatus, the absolute phase of the signal points of the received signal is detected by a phase detecting method having a high detection accuracy when demodulating the received signal, so as to suppress the undesirable effects of the error caused by the noise, even in a case where the reception state of the receiver apparatus is poor. However, the detection speed of the phase detecting method having the high detection accuracy is slow. Consequently, there is a problem in that a relatively long time is always required to detect the absolute phase, regardless of the reception state of the receiver apparatus.
Accordingly, it is a general object of the present invention to provide a novel and useful demodulating method and receiver apparatus, in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide a demodulating method and a receiver apparatus which can improve the detection accuracy and the detection speed of the absolute phase of the signal points of the received signal, regardless of the reception state of the receiver apparatus.
Still another object of the present invention is to provide a demodulating method for demodulating a received signal received by a demodulator unit by detecting an absolute phase of signal points of the received signal, comprising a first step of detecting the absolute phase by a first phase detecting method, a second step of detecting the absolute phase by a second phase detecting method in parallel with the first step, where the second phase detecting method has a slower detection speed or a higher detection accuracy than the first phase detecting method, and a third step of determining the absolute phase based on a phase detection result of the first step when phase detection results of the first and second steps are the same, and determining the absolute phase based on the phase detection result of the second step when the phase detection results of the first and second steps are different. According to the demodulating method of the present invention, it is possible to improve the detection accuracy and the detection speed of the absolute phase of the signal points of the received signal, regardless of the reception state of the receiver apparatus.
A further object of the present invention is to provide a receiver apparatus having a demodulator unit which demodulates a received signal by detecting an absolute phase of signal points of the received signal, wherein the demodulator unit comprises a first detector part detecting the absolute phase by a first phase detecting method, a second detector part detecting the absolute phase by a second phase detecting method in parallel with the first detector part, where the second phase detecting method has a slower detection speed or a higher detection accuracy than the first phase detecting method, and a phase determination part determining the absolute phase based on a phase detection result of the first detector part when phase detection results of the first and second detector parts are the same, and determining the absolute phase based on the phase detection result of the second detector part when the phase detection results of the first and second detector parts are different. According to the receiver apparatus of the present invention, it is possible to improve the detection accuracy and the detection speed of the absolute phase of the signal points of the received signal, regardless of the reception state of the receiver apparatus.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.